The present invention relates to battery packs and batteries that provide increased heat dissipation and particularly relates to lithium-ion battery packs and batteries having a high true surface area to provide increased heat dissipation.
Lithium-ion batteries have found increased use in high power applications such as in automobiles and other vehicles. In these applications, several lithium-ion batteries are typically provided in series and/or in parallel within a battery pack to provide the desired amount of power.
One major problem with the use of lithium-ion batteries in these high power applications is that the batteries within the battery packs can become hot when the batteries are charged or discharged at high rates or when the batteries are short-circuited. If this heat is not properly transferred from the battery pack, the heat accumulates within the battery pack causing xe2x80x9cthermal runawayxe2x80x9d within the batteries. xe2x80x9cThermal runawayxe2x80x9d can be characterized by an uncontrolled rise in temperature that leads to serious safety hazards such as fire or even explosion risks. Because of the importance of safety in these high power applications, there is a need to prevent xe2x80x9cthermal runawayxe2x80x9d in lithium-ion batteries.
The present invention is directed to a battery pack or battery that provides excellent heat dissipation, especially compared to conventional battery packs or batteries, thus increasing the safety of these devices in high power applications. In addition, the present invention provides an inexpensive method of increasing the heat dissipation of battery packs and batteries.
In accordance with the invention, the smooth surfaces of conventional battery packs and batteries are replaced with surfaces having high true surface areas. Specifically, the present invention is directed to a battery pack and/or a battery having a surface with a high true surface area such that the surface roughness (R), defined by the ratio of the true surface area of the surface to the apparent surface area of the surface, is greater than or equal to about 1.2. The present invention is particularly useful for battery packs and batteries that have the tendency to experience heat accumulation such as lithium-ion battery packs and batteries.
According to one embodiment of the invention, the present invention includes a battery pack for holding a plurality of batteries, the battery pack having a surface with a high true surface area, wherein the surface roughness (R), defined by the ratio of the true surface area of the surface to the apparent surface area of the surface, is greater than or equal to about 1.2. Preferably, R is greater than or equal to about 1.5, and more preferably, greater than or equal to 2.0. The surface of the battery pack having a high true surface area can be the outer surface, the inner surface, or both. The surface can be a rough surface or can include a plurality of indentations or raised areas to produce the desired values for R. Preferably, the surface has a scale of surface roughness of less than or equal to about 0.5 mm. In addition to increasing the heat dissipation by increasing R for the surface, the surface can be formed of a material having a high emissivity to provide increased heat dissipation. Preferably, the battery pack is formed of material having an emissivity of greater than about 0.70, more preferably greater than about 0.85. The outer surface of the battery pack can also include a label, preferably a heat dissipative label, e.g., a label having an outer surface with a high true surface area or a label having an emissivity of greater than about 0.70, preferably greater than 0.85. The battery packs of the invention can include a plurality of batteries, such as lithium-ion batteries.
According to another embodiment of the invention, the present invention includes a battery, preferably a lithium-ion battery, having a high true surface area such that the surface roughness (R), defined by the ratio of the true surface area of the outer surface to the apparent surface area of the outer surface, is greater than or equal to about 1.2. Preferably, R is greater than or equal to 1.5, and more preferably greater than or equal to 2.0. In addition, the outer surface preferably has a scale of surface roughness of less than or equal to about 0.5 mm. The outer surface can be rough or can include a plurality of indentations or raised areas to produce the desired values for R. Moreover, the outer surface of the battery can be formed of a material having a high emissivity to provide increased heat dissipation, e.g., having an emissivity of greater than about 0.70, more preferably greater than about 0.85. In addition, the outer surface of the battery can include a label, preferably a heat dissipative label, e.g., a label having an outer surface with a high true surface area or a label having an emissivity of greater than about 0.70, preferably greater than 0.85. The batteries of the invention can also be provided in the heat dissipative battery packs of the invention described above.
These and other features and advantages of the present invention will become more readily apparent to those skilled in the art upon consideration of the following detailed description and accompanying drawings, which describe both the preferred and alternative embodiments of the present invention.